This proposal is designed to allow the primary investigator, Dr. McConnell, to develop the intellectual and technical skills to become an independently-funded research scientist in the field of gastroenterology disease research. Dr. McConnell's research interests focus on Kruppel-like factor 5 (KLF5), a pro-proliferative transcription factor that is highly expressed in epithelial cells of the mammalian gut. Previously, the laboratory has shown that KLF5 is an important factor for promoting proliferation and mediating inflammatory responses in intestinal epithelial cells. Preliminary evidence for this proposal reveals that expression of KLF5 is induced in response to bacterial infection in both cultured intestinal epithelial cells and in mouse colon. From these findings, it is hypothesized that KLF5 promotes tissue homeostasis in the intestinal epithelium by enhancing proliferative and inflammatory responses to bacterial infection or other stress stimuli. Therefore, the specific aims of this study are: (1) To examine the impact of reduced KLF5 expression on colonic epithelial hyperplasia, inflammation and extent of infection following exposure to enteric pathogenic bacteria, using a Klf5-heterozygous mouse model (2) To identify the molecular mechanisms by which KLF5 promotes proliferation and/or inflammation in response to enteric bacterial infection, and (3) To develop an intestinal-specific Klf5 knockout mouse as a definitive model for examining the role of KLF5 in response to various intestinal insults. To address Specific Aim (1), Klf5-heterozygous mice will be infected with the enteric pathogenic bacteria, Citrobacter rodentium. Extent of hyperplasia and inflammation will be assessed by immunohistochemical and biochemical methods over the time course of infection. To address Specific Aim II, the ability of Klf5 to enhance canonical pathways of proliferation and inflammation will be examined. In addition, microarray studies will be conducted to identify downstream targets of Klf5. Finally, for Specific Aim III, a transgenic mouse for intestinal-specific knockout of Klf5 will be generated in order to test the impact of Klf5 expression on responses to various intestinal insults. The proposed research project will contribute to understanding proliferative and inflammatory responses that occur in the intestines following exposure to bacterial pathogens. This knowledge will provide insights in developing treatments for inflammatory bowel disease.